The present invention pertains to a method and apparatus for optically detecting defects in transparent objects, making it possible, through automatic sorting, to eliminate objects which have such defects from the production line.
The invention relates generally to operations in which each transparent object to be inspected is made to stop at one or more successive control stations. At each control station, comprising one or more optical control units, one or more light beams are projected on selected regions of the wall of the object. At the passage of said beams at the wall of the object the light which would be transmitted along set directions is collected. The object is placed in rotation with respect to the control unit, each selected region of the revolving wall of the object being scanned through at least one complete rotation. The deviation in intensity of light collected in the course of this scanning is used to detect the possible presence of certain types of defects and bring about the elimination of objects containing such defects.
The invention pertains more particularly to the detection of defects in objects made of glass, i.e., containers such as bottles, flasks or pots. The defects may be of the type known as glazings in the hollow glass industry. Such glazings, which appear as faults several millimeters long, generally result from a break caused by internal stresses, can involve the entire thickness of the glass wall and have highly varied inclinations.
It is known that such glazings are more likely to appear where there is a variation in form or section of the glass object, and are therefore found especially in the upper parts of containers. Substantially vertical glazings form on the edge of the container, while substantially horizontal glazings form along the flanges, rims or threads. Glazings which form at the shoulder of the container often have the shape of a flattened V.
In the various known optical control processes and devices adjustment of the position of the light emitting and receiving means is generally time consuming, delicate, difficult to reproduce and therefore not very reliable. In practice various optical emitting and receiving means for checking differently shaped objects are attached to swiveling arm support consoles mounted on a common base. This is done to avoid exceedingly costly operations which would result from the use of separate control heads to check differently shaped objects. Adjustment is generally accomplished by successive approximations, the operator responsible for the control looking first, by visual examination, for objects which have defects to be detected, and then setting up the various light emitting means and conjugate receiving means at control stations.
This work is difficult if only because the operator has to function with very low surrounding illumination in order to perceive the light beams. Moreover, because several controls for detecting different types of defects must be effected simultaneously at a single station for reasons of economy, the operator has to avoid interference between the various light beams. The procedures involved are therefore quite delicate, and even when using highly qualified personnel, it is difficult to insure the reproducibility of the settings on separate production runs for a given type of object. Moreover, there are substantial and costly losses of time at each change of production operation.
French Pat. No. 1,588,308 has introduced a significant improvement as concerns these operations by suggesting, in order to eliminate interference between the various light beams and the background noises of internal or external origin such as, for example, variations in the surrounding luminosity, that the light from each optical emitting means on a given control head be given a different modulation, the amplifiers associated with the conjugate optical receiving means being tuned to the modulation of the light to be collected.
It is an object of the present invention to surmount the drawbacks associated with the adjustment of known optical detection processes and devices, by imparting a great ease of application and high degree of reliability and reproducibility to the optical detection of defects in transparent objects. This is accomplished by assigning to each of the various optical emitting means designed to control a given type of defect, and to each of the optical receiving means conjugate therewith, a given orientation and localization previously defined only as a function of the location of the areas to be controlled.
Through tests using statistical analyses to compare the results of direct visual controls and controls obtained using the above-described methods on objects having highly varied shapes and sizes, it has been determined that the installation of the various optical emitting and receiving means required can be standardized and directly related to the shape and size of the object to be inspected.